Serve up schema when Graphiql endpoint is running

[ndarilek]

Hey, really enjoying using this plugin. One thing I'd like to add locally during development is autocompletion/typechecking of GQL queries. There are VS Code extensions for this, but they require access to the schema. async_graphql lets you export it, but that'd be another thing I have to remember to do and commit whenever it changes.

It looks like the extension can retrieve the schema from a URL, however. If the plugin is configured to use graphiql, I wonder if it might also serve up the SDL with the correct content-type so the extension can be connected directly to the running app for the schema? I imagine it can probably just be rolled into the graphiql config since a) it's so low-overhead and b) anyone wanting one might also appreciate the other.

Thanks again.